In electronic component mounting apparatuses, for mounting such electronic components as QFPs or connectors with narrow lead pitches and narrow lead widths, it has been conventional practice to execute automatic inspections for lead floats of components before placing the components onto the printed circuit board.
U.S. Pat. No. 5,200,799 representing the closest prior art from which the invention proceeds discloses a system for inspecting a condition of parts packaged on a printed-circuit board which system includes a position detecting device to receive scattered light due to illumination of the printed-circuit board with a laser beam and convert the received scattered light into a position signal. This position signal is used for obtaining luminance data and at least two height data of the parts on the printed-circuit board. Proper height data of the parts are determined on the basis of the difference between the two height data. The inspection system determines the package condition by comparing the final height data with predetermined reference data.
Accordingly, such optical inspection system checks the presence of poor conditions of mounted parts on a substrate such as position inaccuracy, lacks, rising and soldering fault of parts packaged or installed on the printed-circuit board.
FIGS. 9A-9D are mounting process diagrams of an electronic component mounting apparatus according to a further prior art. In most of the prior art electronic component mounting apparatus, electronic components with narrow lead pitches are mounted through a sequence of processes as shown in FIGS. 9A-9D. More specifically, in a step shown in FIG. 9A, an electronic component 2 accommodated on a tray 3 is suction-picked up by a head section 7 of the mounting apparatus. Then, in a step shown in FIG. 9B, an image of the sucked-up electronic component 2 is picked up by a positioning camera 47, and the electronic component 2 is positioned by using an image processing apparatus, by which positioning information thereabout is obtained.
In a step shown in FIG. 9C, with the use of the positioning information acquired in the step of FIG. 9B, the electronic component 2 is subjected to a coplanarity check by a lead float sensor 48 of transmission type or otherwise has an image picked up at an end portion or end portion shadow of a lead by a coplanarity checking camera 49 so that the image is subjected to a coplanarity check by the image processing apparatus.
With no abnormality found as a result of this check, in a step shown in FIG. 9D, a corrective calculation for a printed circuit board 9 as well as the electronic component 2 to be mounted thereon is executed based on the positioning information acquired in the step of FIG. 9B. Then, the electronic component 2 is placed to a specified position on the printed circuit board 9.
However, with the electronic component mounting apparatus of the prior art as described above, in the case where components are mounted through a sequence of processes to be performed in the steps as shown in FIGS. 9A-9D, because the positioning camera 47 in the step of FIG. 9B and the lead float sensor 48 or the coplanarity checking camera 49 in the step of FIG. 9C are installed physically separately and spaced from each other, there is a need of mechanically positioning the components in the step of FIG. 9C by using positioning information acquired in the step of FIG. 9B, so that the processes in the individual steps could not be simultaneously carried out, inevitably resulting in serial processing, while the components to be mounted need to be treated for move, stop, ascent/descent or other movements for the individual steps. As a result, including the operating time for the move, stop, ascent/descent or other movements of the mounting components, the processing time in the steps of FIG. 9B and FIG. 9C would have a direct effect on the whole mounting time, such that the whole mounting time would be increased by the operating time for those movements.This is disadvantageous.
Besides, when a coplanarity check is performed by the transmission-type lead float sensor 48 as in the step of FIG. 9C, it would be necessary to scan individually four physical edges of a component to be mounted, where the processing time therefor is usually 1 to 3 seconds or so. This prolonged processing would result in a great demerit in mounting a large number of QFPs or connectors, in particular. Meanwhile, also when a coplanarity check is carried out by using the coplanarity checking camera 49, a long time would be required for the coplanarity check, like the foregoing case, on account of the focusing of the camera or the capture of divisional images due to lack of resolution or the like. This also would prolong the mounting cycle time.